Global Biogeochemical Cycles最新文献

Zinc (Zn) is biogeochemically important due to its crucial role in biological processes. In the global ocean, there is an apparent coupling between the concentrations of zinc and silicon (Si), and the ratio between their concentrations is nearly constant in the global ocean. However, this coupling is observed to be disrupted locally for example, in the subarctic North Pacific (NP) Ocean. The aim of the current study was to investigate the roles of uptake parameters, continental-shelf supply, and regeneration of Zn on the observed Zn-Si decoupling in the subarctic NP, employing two distinct circulation fields. Model experiments using two different circulation fields led to the two different conclusions about the cause of the Zn-Si decoupling: continental-shelf supply or regeneration. A comparison between the two circulation fields revealed that older water mass in the NP and greater POC export there led to more regenerated Zn and a higher probability of decoupling without the continental shelf supply. For more quantitative evaluation on relative important of regeneration and continental-shelf supply, both refining biogeochemical models and a circulation field that realistically reproduces regenerated nutrient distribution are required.

Seagrasses are key carbon sinks in the biosphere and, when intentionally conserved or restored, constitute a promising natural solution for climate change mitigation. Unfortunately, they are also experiencing major anthropogenic and climatic pressures that can lead to seagrass degradation or even result in difficult-to-reverse abrupt shifts (i.e., tipping point responses) to complete loss. Although the possibility of tipping point responses in seagrass ecological dynamics has been acknowledged, the potential cascading effect of tipping points on biogeochemical dynamics, shifting seagrass ecosystems from carbon sinks to carbon sources, remains largely unexplored. In this context, we developed a mechanistic stoichiometric model that couples ecological and biogeochemical functioning to assess the effects of three major stressors—mechanical damage, eutrophication, and warming—on the carbon storage capacity of seagrass ecosystems. After parameterizing our model for the Mediterranean seagrass Posidonia oceanica (L.) Delile, we explored these stress cases to identify the processes and feedbacks that can cause ecological tipping points leading to changes in biogeochemical dynamics. The model shows that when ecological tipping points occur, they cascade into biogeochemistry and precipitate abrupt losses of carbon storage. Importantly, even without a tipping point, carbon storage still declined abruptly rather than gradually along stressor gradients. Yet, the dynamics of carbon losses depended on the type of stressor, indicating the need to further test the relative contribution of biotic and abiotic drivers in shifting seagrasses from carbon sinks to carbon sources.

This study synthesizes the budgets of three greenhouse gases (GHG, namely CO₂, CH₄, N₂O) for Russia over two decades (2000–2009 and 2010–2019) using bottom-up and top-down approaches, as part of the Regional Carbon Cycle Assessment and Processes, Phase 2 (RECCAP2). Published estimates of natural sources and sinks of these GHGs in Russia vary widely. Here, bottom-up estimates are based on eddy covariance measurements, the Integrated Land Information System of Russia (ILIS-LEA), field data, Dynamic Global Vegetation Models (DGVMs), and regional models. The bottom-up approach estimated Net Ecosystem Exchange (NEE) at −0.64 ± 0.17 and −0.57 ± 0.14 Pg C yr⁻¹, for decades 2000–2009 and 2010–2019, respectively. Top-down atmospheric inversions provide similar NEE carbon flux estimates with comparable uncertainties at −0.56 ± 0.26 and −0.73 ± 0.27 Pg C yr⁻¹ for the two decades. Differences between these approaches arise from distinct flux components and structural assumptions. ILIS-LEA indicates a slightly declining carbon sink in 2010–2019, driven by increased disturbances. In contrast, DGVMs suggest a stable carbon sink over both decades but they do not fully simulate the effects of disturbances and recovery. Top-down inversions reveal an increasing CO₂ sink, suggesting with additional observed constraints on biomass carbon increment that soil and non-forest biomes absorb more carbon than predicted by DGVMs and ILIS-LEA models. A Bayesian averaging approach estimates natural ecosystems acting as a GHG sink with a land-to-atmosphere flux of −1.55 ± 0.91 and −1.47 ± 0.82 Pg CO₂-eq. yr⁻¹. Accounting for both natural and anthropogenic emissions across the Russian territory shifts the net GHG balance to a source around 1.2 Pg CO₂-eq. yr⁻¹.

Atmospheric deposition is an important pathway for delivering micronutrient and pollutant trace elements (TEs) to the surface ocean. In the central Arctic, much of this supply takes place onto sea ice during winter, before eventual delivery to the ocean during summertime melt. However, the seasonality of aerosol TE loading, solubility, and deposition flux are poorly studied over the Arctic Ocean, due to the difficulties of wintertime sampling. As part of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, aerosols collected during winter and spring (December–May) were analyzed for soluble, labile, and total TE concentrations. Despite low dust loading, mineral aerosol accounted for most of the variation in total Fe, Al, Ti, V, Mn, and Th concentrations. In contrast, soluble TE concentrations were more closely linked to non-sea-salt sulfate, and Fe solubility was significantly higher during Arctic winter (median = 6.5%) than spring (1.9%), suggesting an influence from Arctic haze. Beryllium-7 data were used to calculate an average bulk deposition velocity of 613 ± 153 m d⁻¹ over most of the study period, which was applied to calculate seasonal deposition fluxes of total, labile, and soluble TEs to the central Arctic. Total TE fluxes (173 ± 145 nmol m⁻² d⁻¹ for Fe) agreed within a factor of two or three with earlier summertime estimates, with generally higher wintertime concentrations offset by a lower deposition velocity. Cumulative seasonal deposition of total, labile, and soluble Fe to the central Arctic Ocean was calculated at 25 ± 21, 5 ± 3, and 2 ± 2 μmol m⁻², respectively.

Ocean acidification (OA) threatens coral calcification by reducing the carbonate ion concentration that corals need to build their skeletons. However, assessments of the impacts of long-term OA are scarce, limiting our understanding of the response and acclimatization of corals to high pCO₂ levels. Here we present a 42-year (1968–2010) seasonal δ¹¹B and B/Ca records from Porites corals at Dongsha Atoll, located in the northern South China Sea. Our results reveal a rapid decline in seawater pH over this period, at a rate of −0.0021 ± 0.0008 pH units per year. Of special interest is that the interannual variability in seawater pH appears to be primarily co-regulated by hydrological changes in the Pearl River and fluctuations in the strength of Kuroshio intrusion. These factors are linked to large-scale climate systems and interannual-to-decadal variability, including the Pacific Decadal Oscillation, El Nino-Southern Oscillation, and East Asian Winter Monsoon. Meanwhile, reconstructed carbonate chemistry from the coral calcifying fluid suggests that Porites corals at Dongsha Atoll are able to physiologically modulate their internal pH. This up-regulation of internal pH not only buffers seasonal fluctuations in the aragonite saturation state and sustains stable calcification rates year-round, but also aids in long-term resistance to the detrimental effects of OA.

In their 1999 paper “Widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling,” Sharp and co-authors initiated a paradigm shift from glaciers viewed as abiotic systems to glacier environments hosting active microbial communities and corresponding biogeochemical cycling. Since then, the field of glacier biogeochemistry has sought to elucidate how these microbes function and the consequences of their activity in glacial and proglacial environments, and for global biogeochemical cycles. Subsequent research has supported the existence of active biogeochemical cycling by the “glacial microbiome.” Paradoxically, dissolved organic matter (DOM) exported in glacier meltwater is both ancient and a labile source of organic carbon that may be readily incorporated into downstream ecosystems. Further, DOM that has been characterized in glacier systems (using both fluorescence spectroscopy and ultrahigh resolution mass spectrometry) from different locations shares specific fluorescence and molecular formulae characteristics, hinting at a potential commonality in “glacial DOM.” The recent manuscript “Gradients of Deposition and In Situ Production Drive Global Glacier Organic Matter Composition” (Holt et al., 2024, https://doi.org/10.1029/2024gb008212) addresses these two observations by employing Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to characterize DOM composition at the molecular level from glacier sites located around the globe. The use of both the powerful FT-ICR MS technique and an unparalleled global glacier data set offers a unique insight into glacier DOM variability and commonality, and the source of ancient and/or labile DOM in glacier runoff. Further, the study provides an impetus for specific future lines of investigation.

Glacial retreat due to climate warming alters the pathway through which meltwater enters Arctic fjords. In the Tyrolerfjord–Young Sound system (NE Greenland), meltwater is delivered by two contrasting rivers: the Tyroler River, which flows directly from the glacier into the fjord, and the Zackenberg River, which passes through a proglacial lake. We investigated the impact of these different glacial sources on the pelagic system and fjord sediment biogeochemistry, with a focus on carbon and iron cycling. We quantified particulate organic carbon and particulate organic nitrogen, as well as δ¹³C and δ¹⁵N of the organic matter in the suspended and sinking fractions in the water column. In sediment, we quantified total organic carbon (TOC) and total nitrogen, δ¹³C and δ¹⁵N of the organic matter, porewater concentrations of Fe, Mn, and different fractions of solid-phase Fe, O₂ microprofiles and sulfate reduction rates. We find that the passage through a proglacial lake decreases the impact of the glacier on the fjord, as the lake acts as a trap for glacial material, decreasing sediment input to the fjord system. In the fjord sediments, a stronger redox-cycling of iron was found further away from the rivers, which is mainly driven by the higher TOC content. Overall, our data suggest that, with glacial retreat, the impact of glaciers on the marine and the benthic systems in fjords will become weaker, and reduce long-term carbon sequestration in Arctic fjord sediments.

Shifts in vegetation phenology affect photosynthesis and productivity, further influencing ecosystem carbon and hydrological cycles. Over recent decades, widespread advancements in the start of the growing season (SOS) have been found to advance the peak of the growing season (POS) and enhance vegetation growth under global warming. Understanding vegetation growth dynamics from SOS to POS (i.e., start-to-peak growth) is crucial because this period represents a critical phase of carbon uptake and ecosystem productivity, directly impacting seasonal and annual climate-biosphere feedback. However, the effect of SOS on vegetation growth, especially start-to-peak growth, remains largely unknown. Using MODIS NDVI, ground FLUXNET data set, and meteorological data (2001–2022) across the Northern Hemisphere (>30°N), we found that SOS advanced by 0.11 days per year, while start-to-peak growth, indicated by the sum of daily NDVI from SOS to POS, increased by 0.13 units per year. Notably, earlier SOS significantly enhanced start-to-peak growth in 55.64% of vegetated pixels (p < 0.05). Critically, the earlier SOS was associated with a longer SOS-POS duration and lower vegetation growth rates, suggesting that the extended SOS-POS duration contributed to the observed increased start-to-peak growth. Climatic conditions, especially colder temperatures, slowed growth rates, particularly at mid-latitudes. This slowing of growth rates was observed across various vegetation types, although the magnitudes of the reduction varied among them. Overall, these findings enrich our understanding of how start-to-peak growth responded to spring phenology and climate change, offering valuable insights into future predictions of terrestrial ecosystem dynamics under global change.

Earth system models are increasingly adopting multi-layer soil frameworks to improve simulations of vertical carbon distribution. A critical parameter in these models is the e-folding depth (z_τ), which quantifies the rate at which soil organic carbon (SOC) ages with depth. Specifically, z_τ represents the soil depth at which carbon becomes e-times older (≈2.7 times older) than surface carbon. Despite its importance, most models assume constant z_τ within biomes, leaving its spatial variability largely unclear. To test this assumption, we collected multi-layer soil samples across eight forest plots spanning a subtropical montane elevational gradient (427–1,474 m) and employed radiocarbon dating to quantify vertical SOC aging patterns. Our results revealed a robust exponential increase in SOC age with depth at all elevations, alongside a 66% decline in z_τ from 78.6 cm at the base to 26.4 cm at the summit. This indicated that a 1-m increase in soil depth approximately amplified SOC age by 4-fold at the lowest elevation and 44-fold at the highest position. Despite significant changes in vegetation along the elevational gradient, vegetation type did not play an essential role in controlling z_τ variability. Instead, this elevational dependence of z_τ was primarily driven by soil water content (22.2% of variability explained), mean annual temperature (19.7%), and soil carbon-to-nitrogen ratio (19.0%). These findings suggest z_τ as an elevation-sensitive sentinel of soil carbon dynamics, urging models to incorporate its variability for projections of soil carbon persistence under climate change.

Compound extremes of temperature and acidity that extend over substantial fractions of the water column can be particularly damaging to marine organisms, as they experience not only additional stress by the potentially synergistic effects of these two stressors, but also a reduction in habitable vertical space. Here, we detect and analyze such column-compound extremes (CCX) in the Southern Ocean between 1980 and 2019, and characterize their duration, intensity, and spatial extent. To this end, we use daily output from a hindcast simulation of the Regional Ocean Modeling System (ROMS), coupled with the Biological Elemental Cycling (BEC) model. We first detect extremes in temperature and acidity ([$��H^{+}�$]) within the top 300 m using a relative threshold of 95% and then identify CCX where conditions are extreme for both stressors for at least 50 m of the water column. When analyzed on a fixed baseline, positive trends in ocean warming and acidification caused CCX to last longer, intensify, and expand throughout the Southern Ocean. In the Antarctic zone, CCX expanded between 1980 and 2019 more than ten times in volume, lasted up to 120 days longer, and doubled in anomaly. Some of the largest and longest events occurred in Antarctic Marine Protected Areas (MPAs), covering more than 200,000 km² and persisting for over 500 days. CCX in the Subantarctic and Northern zones quadrupled in volume and increased by more than 30% in anomaly. Across the Southern Ocean, the increasing occurrence of CCX exacerbates the risks to marine ecosystems from warming and acidification.